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Developing management options

The majority of tussock grassland research has focussed on determining the vegetation history of the mountain lands, and how pastoral management practices have influenced vegetation succession patterns. Only recently has grasslands research started to look at the issue of progressive successional changes occurring on retired land (i.e. what vegetation changes will take place when tussock grasslands are retired from grazing and burning). In addition, the majority of studies have focussed on determining the impacts of pastoral use on narrow-leaved snow tussock grasslands, the most widespread tussock grassland type in the eastern parts of the Main Divide. Obviously, there are many information gaps which need to be filled.

High altitude tussock grasslands generally require less active management than communities at lower altitudes. High altitude areas tend to be less modified, as the more extreme growing environment makes such areas less attractive for pastoral development. At a workshop on conservation management of tussock grasslands held in June 1996, ecologists and land managers agreed that most Chionochloa grasslands at high altitude required minimal active management (weed and pest control), and that a "no grazing with fencing" approach would adequately maintain the conservation values.

Mid-altitude tussock grasslands generally require more active management than such communities at higher altitudes, because there is a higher risk of weed spread and woody plant regeneration. These areas have been attractive for pastoral development because the combination of adequate rainfall and soil temperatures promotes moderately good plant growth.

Low altitude areas have been the focus of farm development programmes, which may include cultivation, land drainage, tree planting, and exotic pasture establishment. The majority of lower altitude tussock grasslands have therefore already been partially modified or totally removed. Existing tussock grasslands are often at high risk of weed invasion from surrounding farmland. Such areas therefore generally require more active management than communities at higher altitudes.

for more information on environmental gradients that determine the distribution of tussock grassland types, or the management factors that have influenced the characteristics of tussock grasslands.

if you want further information on a generalised model for vegetation change, east of the Main Divide.

Chionochloa is a long lived bunch grass, which flowers irregularly in terms of both frequency and intensity of flowering. Seedlings only establish in the year following flowering, which occurs on average 1 in 5 years. The onset of flowering is climatically induced- a warm summer triggers flowering.

Where diversity of herbs and grasses growing between tussocks is considered desirable, the tussock canopy will have to be disturbed to prevent them overtopping the intertussock plants. Burning and grazing are the cheapest tools for achieving this, and have been part of pastoral management for the past 150 years.

Tall tussock grasslands are poorly adapted to mammalian grazing, as it decreases the reproductive vigour of adult tussocks (O'Connor, 1963; Mark, 1965; Mills et al., 1989). While native birds (e.g. takahe) have fed on tussocks since primaeval times, they have a different feeding mode to that of domestic and feral animals which graze the tussocks. Native birds have been shown not to cause the decline in tussock vigour ( i.e. reduction in tillering and productivity) than grazing mammals do today (Mill et al., 1989).

Where diversity of herbs and grasses growing between tussocks is considered desirable, the tussock canopy will have to be disturbed to prevent it becoming too dense, and competitive. Burning and grazing are the cheapest tools for achieving this, and have been part of pastoral management for the past 150 years.

a) Natural disturbance (1 in 100 year frequency) (W.G. Lee, pers comm) Infrequent burning effectively rejuvenates the tussock population of a grassland, through promoting mass flowering, and triggering the germination of some dormant seed, depending on the time period since the last burn. This results in large-scale seedling establishment. The induced burst of reproductive activity effectively suppresses subsequent reproductive activity for several decades. Burning of tussock grasslands retards it's succession to native scrubland, but also provides an opportunity for the invasion by other plant species.

Burning has been suggested as a conservation management tool by conservation managers and ecologists, where it is desirable to keep the tussock canopy open, so as to maintain the diversity of intertussock herbs and grasses. Numerous reviews have been made to summarise research findings relating to the effects of burning on tussock grassland communities (Basher et al.. 1990; McKendry & O'Connor 1990; Hughes et al.. 1995, and Allen et al.. 1996). The latter report reviewed overseas and New Zealand literature pertaining to the use of fire for conservation management. Most studies have focussed on the impact of fire on narrow-leaved snow tussock grassland (C. rigida). In the absence of grazing, an initial pulse of vigorous regrowth in the surviving plants and an increase in diversity, especially of herbs, is documented. This is followed by a decline on growth rates and diversity as the tall tussocks increase in stature. Woody plants may also increase.

Researchers have found that, even after 15 years, the total biomass of burnt tussock is still only 65% of unburnt tussock biomass (Payton et al., 1986). Gitay et al. (1992) suggest that full recovery of tussock stature, and size and density of tillers may take 20 - 25 years after a fire. Lee et al., (1996) concluded that recovery of narrow-leaved snow tussock after burning takes at least 20 years, and grazing, particularly in the first few seasons after burning, reduces the number and size of tillers and tussocks in the grassland and greatly slows the rate of tussock recovery. The soil nutrient pulse associated with burning enhances tussock growth in the first 2 years, but changes in biochemical features (e.g. lower soil microbial C/microbial N ratio) suggest that soil quality will decline for some as yet unknown period. The condition of the narrow-leaved snow tussocks, particularly whether they have recovered from previous disturbances, can be determined using an index involving tiller weight, tiller length and canopy cover.

Because there is little known about the impact of fire on intertussock species, Chionochloa species other than C. rigida, or the burn interval appropriate for conservation management, ecologists and conservation managers believe the best approach is to only burn a small area of the whole grassland area a time. Patch burning is an insurance policy in case an unexpected or undesirable successional pathway occurs as a result of the burn. It also recognises that, while large areas of grassland would have burnt as a result of natural fires in pre-human times, such a practice today would put too much life and property at risk.

Lee et al., (1996) developed a tussock recovery index for narrow-leaved snow tussock grasslands in Otago. Tussocks were considered to have adequately recovered from the effects of fire when:

• canopy area was greater than 50% surface area (or 70% on a linear basis)
• tiller weights (when dried) were greater than 1.2gm dry weight
• tiller length was greater than 0.60m.

if you want more information on the tussock recovery index

Buffering

The relationship an area managed for conservation purposes has with it's surrounding landscape is important. Ideally, the area should be surrounded by land which will buffer it from external influences which may compromise the conservation values.

• act as a fire break, thereby protecting neighbouring land from wild fires occurring in dense tussock grasslands, or preventing controlled fires on pastoral land inadvertently burning an area managed for conservation.
• protect the area from inadvertent AOSTD drift from neighbouring land
• protect the area in terms of the hydrological processes. A wet red tussock grassland or wetland is dependent on a high water table. A buffer zone may have to include a significant part of the upstream catchment to protect those hydrological processes
• help reduce the rate of spread of some weed species into the area e.g. intensive grazing between a forest and an ungrazed tussock grassland helps reduce the establishment of wilding trees from that forest.

Weed spread is less likely to be a problem at high altitudes, except where significant disturbance has taken place e.g. sheep camps, or at sites which are downwind of conifer stands (plantation or wilding forests). Periodic monitoring of the area is necessary to determine whether weed species are coming into the area, and whether they are reaching problem levels. An assessment of the feasibility of controlling the weeds will then have to be made.

for more specific information on weed control

Vegetation succession

if you want more information on factors influencing vegetation succession (includes model for vegetation succession).

The regeneration of native tree and shrubland species is not likely at high altitudes which are above the historic tree line. However, such regeneration will occur in "induced" tall tussock grasslands occurring below the historic tree line, where there is a suitable seed bank present.

Whilst rabbits are usually absent, or occur in very low numbers, in relatively unmodified tall tussock grassland, they can become prevalent in grasslands modified by sheep grazing and burning activities, especially in drier areas such as the southern end of the Ben Ohau Range. Rabbit grazing reduces tussock cover and stature (Norbury, 1996).

The management guidelines suggested are based on the best information available today. However, since most of the research done has dealt with how pastoral management influences succession in mainly narrow-leaved snow tussock grasslands, there are many gaps in our knowledge. We don't really know what successional path many of the tussock grasslands will take under different management regimes (e.g. destocking) or climatic conditions. While the majority of tall tussock grasslands will receive minimal active management, save animal exclusion, weed and fire control, these in themselves cost time and money. To ensure that the management practices used are in fact achieving the desired management goal, it is crucial that the vegetation condition and composition are monitored, as are the status of weed and animal pest populations. Management may have to be changed in response to the findings of such on-going monitoring.

for more information on monitoring in tussock grasslands

• All references
• Short tussock grasslands
• Tall tussock grasslands
• Burning studies